UX: Apply `btn-flat` class to flat buttons on posts

app/assets/javascripts/discourse/widgets/button.js.es6

@@ -1,7 +1,8 @@
 import { createWidget } from 'discourse/widgets/widget';
 import { iconNode } from 'discourse/helpers/fa-icon-node';
 
-export default createWidget('button', {
+
+const ButtonClass = {
   tagName: 'button.widget-button',
 
   buildClasses(attrs) {
@@ -59,4 +60,10 @@ export default createWidget('button', {
     }
     return this.sendWidgetAction(attrs.action);
   }
-});
+};
+
+export default createWidget('button', ButtonClass);
+
+createWidget('flat-button', jQuery.extend(ButtonClass, {
+  tagName: 'button.widget-button.btn-flat'
+}));

app/assets/javascripts/discourse/widgets/post-menu.js.es6

@@ -230,7 +230,7 @@ export default createWidget('post-menu', {
     if (builder) {
       const buttonAtts = builder(attrs, this.state, this.siteSettings);
       if (buttonAtts) {
-        return this.attach('button', buttonAtts);
+        return this.attach('flat-button', buttonAtts);
       }
     }
   },

app/assets/stylesheets/desktop/topic-post.scss

@@ -53,17 +53,23 @@ section.post-menu-area {
 
 nav.post-controls {
 
-    .like-count {
-      font-size: inherit;
-      margin-right: -5px;
-    }
+  padding: 0;
 
-    padding: 0;
-    .highlight-action {
-      color: dark-light-choose(scale-color($primary, $lightness: 60%), scale-color($secondary, $lightness: 40%));
-    }
-    a, button {
+  .like-count {
+    font-size: inherit;
+    margin-right: -5px;
+  }
+
+  .highlight-action {
+    color: dark-light-choose(scale-color($primary, $lightness: 60%), scale-color($secondary, $lightness: 40%));
+  }
+
+  a, button {
     color: dark-light-choose(scale-color($primary, $lightness: 75%), scale-color($secondary, $lightness: 25%));
+
+    i.fa {
+      opacity: 1.0;
+    }
     margin-right: 2px;
     display: inline-block;
   }

app/assets/stylesheets/mobile/topic-post.scss

@@ -47,6 +47,9 @@ span.badge-posts {
 
 nav.post-controls {
   clear: both;
+  i.fa {
+    opacity: 1.0;
+  }
 }
 
 .who-liked {